More changes.

Move libfmt, libutf into subdirectories of lib9. Add poll-based socket i/o to libthread, so that we can avoid using multiple procs when possible, thus removing dependence on crappy pthreads implementations. Convert samterm, acme to the single-proc libthread. Bring libcomplete, acme up-to-date w.r.t. Plan 9 distribution.

Until I hear otherwise, Refs aren't used enough to merit their own assembly. They are now implemented with locks.

which were completely bogus. (Libthread used to ignore them but not anymore. Maybe we really should ignore them, but that breaks Venti, which needs *really* big stacks.)

remove clumsy stack hack. fix exec. fix nthreads maintenance. fix threadexitsall not to kill self. add sun support.